Vitamin A is important for the immune system, vision, reproduction, and cell growth. There is now a growing body of evidence that Vitamin A metabolism plays a key role in exerting control over energy balance and thermogenesis with the potential for new insights into obesity and its treatment.
A research team led by Florian Kiefer from MedUni Vienna’s Division of Endocrinology and Metabolism studied the effects of cold exposure on systemic Vitamin A levels in humans and mice and the relevance of intact retinoid transport on cold-induced adipose tissue browning. The results showed that Vitamin A levels increased in humans and mice when subjected to cold ambient temperatures.
This helps convert the white adipose tissue or white fat, which is bad into the brown fat or brown adipose tissue (BAT) that stores energy in smaller quantities and stimulates fat burning and heat generation also known as cold thermogenesis.
This “fat transformation” is usually accompanied by enhanced energy consumption and is therefore considered a promising approach for the development of novel obesity therapeutics as it can significantly reduce their risk of developing obesity. The study has now been published in the leading journal Molecular Metabolism.
There are at least two types of fatty depots in humans and mammals- white and brown adipose tissue. The excess calories during obesity are mainly stored in white fat or white adipose tissue (WAT). Brown adipose tissue (BAT) dissipates energy to produce heat. Thus, it has the potential to regulate body temperature by thermogenesis.
In humans, the overwhelming proportion of the body fat that is more than 90% is made up of white fat and is located at the abdomen, bottom, and upper thighs. Brown fat is usually found around the shoulders, neck, and spinal cord. Converting white into brown fat could be a new therapeutic option to combat weight gain and has the potential for new insights into obesity and its treatment.
A research group led by Florian Kiefer from the Division of Endocrinology and Metabolism, Department of Medicine III at MedUni Vienna has now demonstrated that moderate application of cold increases the levels of vitamin A and its blood transporter, retinol-binding protein, in humans and mice.
Most of the vitamin A reserves are stored in the liver and cold exposure seems to stimulate the redistribution of vitamin A toward the adipose tissue. The increase in vitamin A due to exposure to cold led to a conversion of white fat into brown fat also known as (“browning”), ultimately burning more calories.
When Kiefer and his team blocked the Vitamin A transporter retinol-binding protein in mice by genetic manipulation, both the cold-mediated rise in vitamin A and the browning of the white fat were blunted: “As a consequence, fat oxidation and heat production were perturbed so that the mice were no longer able to protect themselves against the cold,” explains Kiefer.
In contrast, the addition of vitamin A to human white fat cells led to the expression of brown fat cell characteristics, with increased metabolic activity and energy consumption.
“Our results show that vitamin A plays an important role in the function of adipose tissue and affects global energy metabolism. However, this is not an argument for consuming large amounts of vitamin A supplements if not prescribed, because it is critical that vitamin A is transported to the right cells at the right time,” explains the MedUni Vienna researcher.
“We have discovered a new mechanism by which vitamin A regulates lipid combustion and heat generation in cold conditions. This could help us to develop new therapeutic interventions that exploit this specific mechanism.”
The study involved scientists from Harvard University, Boston and Rutgers University, New Jersey and was funded by the Austrian Science Fund (FWF), the Vienna Science and Technology Fund (WWTF), and the research fund of the Austrian Diabetes Society.
Source Link: Medical University of Vienna
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